The end wall of a hydraulic cylinder is normally formed with a throughgoing cylindrical hole or passage whose inner surface is spaced radially outward from the outer surface of the piston rod that passes through it. This inner wall is normally formed with various inwardly open grooves that receive various elements. These elements include a relatively hard guide that snugly engages the outer surface of the piston rod to center it in the passage, an outside scraper which prevents anything that has become deposited on the piston rod while it is outside the cylinder from being drawn back into the cylinder, and of course on the inside high-pressure side a gland or seal that prohibits leakage from the cylinder. This seal is normally a so-called cup that is of U-section open toward the inside high-pressure side.
The main problem with such an assembly is obviously that it is complex. If any of its elements fails, it is necessary to disassemble the entire structure. A careful worker also normally also replaces all of the other parts while the assembly is in pieces, as the cost of the parts is relatively small compared to the cost of the labor installing them.